Twitter application was created by Google engineers to promote new Android application UI patterns. It is therefore the reference implementation of action bar pattern. It includes branding, contextual information (see twitter post character count) and fast access to all most used functions on each screen. A promise was made in Google I/O 2010 that source code for this app will be released but that has not happened yet.
Miso uses action bar to indicate running background process on top of providing branding, dashboard access and search access. The refresh button is animated whenever the application is fetching data from servers. Nice touch.
GDD app's action bar has both branding and context in the application. Top part of the bar has Google Developer Day color theme as the bar's main color indicates where inside the application user currently is. In this case the application icon was replaced by home icon.
Android Market application's action bar is combined with the navigation controls. Until the user dives into details of an application the action bar is shown including a styled text to give context to the user. Pressing the Android Market logo will take the user back to front page.